1. Technical Field
This invention relates to the field of Radio Frequency Identification (RFID) tags and labels, and to particular structures of RFID tags and labels and methods of manufacturing them.
2. Background Art
Alien Technology Corporation (“Alien”), of Morgan Hills, Calif., has developed techniques for manufacturing microelectronic elements as small electronic blocks, which Alien calls “NanoBlocks™,” and then depositing the small electronic blocks into recesses on an underlying substrate. To place the small electronic blocks into the recesses, Alien uses a technique known as Fluidic Self Assembly (“FSA”). The FSA method includes dispersing the small electronic blocks in a slurry, and then flowing the slurry over the top surface of the substrate. The small electronic blocks and recesses have complementary shapes, and gravity pulls the small electronics down into the recesses. The end-result is a substrate (e.g., a sheet, a web, or a plate) that is embedded with tiny electronic elements.
There are a number of issued patents which are relevant this technique, including U.S. Pat. Nos. 5,783,856; 5,824,186; 5,904,545; 5,545,291; 6,274,508, 6,281,038, 6,291,896, 6,316,278, 6,380,729, and 6,417,025, all of which the present application incorporates by reference in their entireties. Further information can be found in Patent Cooperation Treaty publications, including WO 00/49421; WO 00/49658; WO 00/55915; WO 00/55916; and WO 01/33621, all of which this application incorporates by reference in their entireties.
FIG. 1 is a simplified flow diagram illustrating a process for embedding a substrate with small electronics using Alien's FSA process. The process starts with CMOS wafers at step 10, which are micromachined into tiny blocks at step 12. These small electronic blocks may be any of a variety of electronic components, such as integrated circuits. The small electronic blocks may be made in a variety of different shapes. FIG. 2 illustrates alternative block shapes 100, 120 and 130. Each is angled on the side, and has an upper portion that tapers down to a narrower lower portion.
Specific examples of small electronic blocks containing microcircuitry and the method of their manufacture are found in the aforementioned Alien Technology patents. The blocks' circuit formation starts with generally standard silicon wafers fabricated by existing IC foundries. The process thereafter separates the wafers into millions of tiny block circuits. A standard backside wafer grind/polish technique is used, and a backside mask defines the block. The blocks are separated from the wafer.
One preferred microstructure block shape comprises a truncated pyramid with a base and four sides. Each side creates an inwardly tapering angle of between about 50° and about 70° with respect to the base, with 54.7° being the preferred angle for the particular device. Each side may also have a height between about 5 μm (microns) and about 200 μm. The base also may have a length between about 10 μm and about 1000 μm and a width between about 10 μm and about 1000 μm.
To receive the small electronic blocks, a planar substrate 200 (FIG. 3) is embossed with numerous receptor wells 210. The receptor wells 210 are typically formed in a pattern on the substrate. For instance, in FIG. 3 the receptor wells 210 form a simple matrix pattern that may extend over only a predefined portion of the substrate, or may extend across substantially the entire width and length of the substrate, as desired.
The substrate material 200 into which the small electronics are to be integrated is typically a plastic film or a glass plate, as noted at step 14 in FIG. 1. At step 16, recesses or holes are formed in the film or plate. The recesses or holes have a shape that is complementary to the shape of the small electronics, such that each small electronic will fit into a corresponding recess or hole.
At step 18, the FSA process is employed to embed the small electronics into the recesses or holes. FIG. 4 illustrates small electronic blocks 100 in slurry 201 that is applied over a sheet or web 200. Gravity will pull a small electronic block into a recess 210 that has a shape that complements the shape of the small electronic block.
During the FSA process, a large number of the microstructure elements 100 are added to a fluid, creating slurry 201 (FIG. 3). The slurry is sprayed on or otherwise flows over the substrate material 200 with the receptor recesses 210. By chance some of the microstructure blocks 100 will fall into and, because of their shape, self align in the recesses 210. Once a microstructure block 100 flows into a recess 210, the microstructure element is retained in the close-fitting recess 210 by hydrodynamic forces. Further details regarding the manufacture of the microstructure blocks and the FSA processes may be found in U.S. Pat. Nos. 5,545,291 and 5,904,545, and PCT/US99/30391 as published at WO 00/46854, the entire disclosures of which are herein incorporated by reference.
After the FSA process, the substrate 200 may be checked for empty recess regions, for example by using an electronic eye attached to a machine capable of viewing the surface of the substrate material. Empty recess regions 210 may be filled, for example as suggested by Alien Technology, by using a robot to place a microstructure element 100 therein.
As FIG. 5 illustrates, the FSA process preferably can be performed as a continuous roll operation by pulling a web of substrate material 200 through a bath of the slurry 201. Vacuum devices 220 and 224 may pull excess fluid and/or impurities off the substrate web 200 at the start and end of the FSA process. Spray devices 222 may be utilized to spray the slurry 201 onto the substrate web 200. The rate at which the slurry 201 is sprayed onto the substrate web 200 may be such that the number of microstructure blocks 100 falling past any given area of the substrate web, is several times the number of the receptor recesses 210 in that area of the substrate material 200.
An excess number of the microstructure blocks 100 may be required in order to obtain full filling of all the receptor recesses 210. The slurry 201 generally may be reused, since the excess microstructure blocks 100 therein generally do not suffer damage by collision with the substrate material or with each other, due to hydrodynamic forces.
One application for a sheet that is embedded with tiny electronic components is to make radio frequency identification (RFID) tags and labels. In ordinary terminology, and as used in the present patent application, a “label” includes a layer of adhesive that “sticks” the label to a substrate, whereas a “tag” has no such adhesive. RFID tags and labels have a combination of antennas, analog and/or digital electronics, and often are associated with software for handling data. RFID tags and labels are widely used to associate an object with an identification code. For example, RFID tags are used in conjunction with security-locks in cars, for access control to buildings, and for tracking inventory and parcels. Some examples of RFID tags and labels appear in U.S. Pat. Nos. 6,107,920, 6,206,292, and 6,262,292, all of which this application incorporates by reference.
Information is stored on the RFID chip. To retrieve the information from the chip, a “base station” sends an excitation signal to the RFID tag or label. The excitation signal energizes the tag or label, and the RFID circuitry transmits the stored information back to the reader. The “reader” receives and decodes the information from the RFID tag. In general, RFID tags can retain and transmit enough information to uniquely identify individuals, packages, inventory and the like. RFID tags can also be used to store information that is written onto the RFID chip during process, such as temperatures or other data types, and logistical histories.
The RFID chip may be a part of a radio-frequency identification transponder that is a part of the RFID tag or label. Radio-frequency identification transponders are widely available in a variety of forms. These devices include a non-volatile memory, such as an EEPROM (Electrically Erasable Programmable Read-Only Memory) semiconductor component integrally contained in the transponder. Stored in the non-volatile memory are encoded data. Inlay transponders are identification transponders that have a substantially flat shape. The antenna for an inlay transponder may be in the form of a conductive trace deposited on a non-conductive support. The antenna has the shape of a flat coil or the like. Leads for the antenna are also deposited, with non-conductive layers interposed as necessary. Memory and any control functions are provided by a chip mounted on the support and operatively connected through the leads to the antenna.
The prior art view of FIG. 6 illustrates an article 300 onto which an RFID label 302 has been adhered. The RFID label includes a principal surface 304 onto which text and/or graphics may be printed, such as text 306. The label 302 may be adhered to the substrate 300 by means of a pressure sensitive adhesive, other types of adhesives known in the label art, or, alternatively, by other means of attachment such as by sewing, heat bonding, fusing, or other conventional attachment methods. The RFID label 302 includes the very small RFID chip that is within the label. The face stock 304 may be any face stock known in the art for labels. For example, the face stock 304 might be printable paper, a coated polymer, such as coated Mylar® film, a printable foil, or any other type of face stock used in the label art. Alternatively, in the case of an RFID tag (not shown), the tag could be secured to article 300 using a wide variety of non-adhesive means, such as a plastic fastener, string, wire, etc.
It will be appreciated from the above discussion that many approaches have been undertaken with regard to RFID tags and labels, and that improvements in such tags and labels, and their methods of manufacture, would be desirable.